1. Field of the Invention
The present invention relates to a radio-frequency circuit module, such as a variable filter circuit module or a variable matching circuit module, which is capable of adjusting frequency characteristics or impedance characteristics for a radio-frequency signal to be transmitted.
2. Description of the Related Art
Currently, various communication devices that transmit and receive a plurality of radio-frequency signals in different frequency bands (communication bands) by using a common antenna for these radio-frequency signals are commercially available. This type of communication device includes a radio-frequency circuit module, such as a variable matching circuit or a variable filter, for performing impedance matching for each communication band. As a variable filter module, the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2012-191521, for example, is available.
The variable filter device (module) disclosed in Japanese Unexamined Patent Application Publication No. 2012-191521 includes surface-mount variable capacitance elements and passive elements including distributed constant lines. In the variable filter module disclosed in Japanese Unexamined Patent Application Publication No. 2012-191521, the surface-mount variable capacitance elements are mounted on a single layer substrate, and the passive elements are formed on the surface of this substrate by using distributed constant lines, thus reducing transmission loss between the passive elements including the distributed constant lines and the variable capacitance elements.
However, the variable filter module disclosed in Japanese Unexamined Patent Application Publication No. 2012-191521 has a large size and occupies a large area since the variable capacitance elements and the passive elements including the distributed constant lines are disposed on the surface of the single layer substrate.
Additionally, line conductors used for a control signal for the variable capacitance elements and line conductors used for a radio-frequency signal for the variable capacitance elements are disposed on the same plane. Accordingly, these line conductors are likely to interfere with each other, thus increasing the possibility that a control signal mix with a radio-frequency signal to be transmitted. That is, isolation characteristics concerning the isolation of a radio-frequency signal (communication signal) from noise are likely to decrease.